The present invention is related to orthopedic implants and is more particularly related to spinal implants.
There have been many efforts directed to providing improved spinal implant devices. For example, U.S. Pat. No. 5,534,029 to Shima discloses an articulated vertebral body spacer including a pair of upper and lower joint pieces inserted between opposing vertebrae. The lower joint piece includes a convex portion formed on a central portion of its upper surface and having a convex sliding contact surface, and a stopper surface surrounding the convex portion. The upper joint piece includes a concave portion formed on a central portion of its lower surface and having a concave sliding contact surface which is in sliding contact with the convex sliding contact surface, and an abutment surface that surrounds the concave portion and abuts against the stopper surface. A cavity for allowing the upper joint piece to pivot in response to movement of the opposing vertebral bodies is formed between the abutment surface and the stopper surface.
DE 3529761 discloses a prosthesis for an intervertebral disc including two plates with a spacer disc therebetween. The two plates each have a concave center and a flat annular rim with spikes. The disc spacer has a convex center and a flat rim with an annular groove. The prosthesis is used for spanning the gap between opposing vertebral faces remaining firmly in place while permitting natural movement of the spine.
U.S. Pat. No. 4,997,432 to Keller discloses a prosthesis including two stop plates and a sliding body arranged therebetween. The outer surfaces of the stop plates have an essentially planar surface provided with tooth-like projection that penetrate into the vertebral bodies to fix the stop plates securely to the vertebral bodies. The opposite side surfaces of the stop plates include essentially spherical-shell-shaped recesses. The sliding core has a spherical-shell-shaped projections corresponding to the spherical-shell-shaped recesses. The stop plates are made of metal and the sliding body is made of a synthetic material.
U.S. Pat. No. 5,562,738 to Boyd et al. discloses an implant device having an ellipsoidally-shaped ball and socket oriented so that their greatest lengths are disposed along a first axis transverse to the anterior and posterior ends and respectively and their shortest lengths are disposed along a second axis which is perpendicular to the first axis along surface. A first joint surface is sloped away from socket while a second joint surface remains flat. The degree of slope determines the amount of relative rotation between joint surfaces and respectively, and the first joint surface is sloped to provide for up to 5xc2x0 of lateral bending in either direction, up to 5xc2x0 of extension and up to 5xc2x0 of Flexion.
Finally, U.S. Pat. No. 5,556,431 to Buttner-Janz discloses an intervertebral disc endoprosthesis that is inserted between two vertebrae and has a bottom plate and a top plate that are connected to vertebral endplates. Referring to FIG. 1, the device includes prosthesis plates and prosthesis core cooperated via spherical surfaces. The core has an edge rim that limits its range of movement and insures, even under extreme conditions cohesion of the prosthesis. The endplate of the prosthesis plates, lie on the end surfaces of the vertebrae and are provided with teeth which, under load, penetrate into the vertebrae and thus secure the prosthesis in situ. Bore holes are arranged symmetrically on both side of the central plane, running from ventral to dorsal, of the vertebrae and in the area of the front edge of the prosthesis plates, to receive bone screws.
In spite of the above-noted advances in the art, there remains a need for an improved vertebral body spacer having enhanced stabilization and bone fusion characteristics. There is also a need for a vertebral body spacer that may be readily packed with bone growth material for facilitating fusion of the spacer with vertebral bodies. In addition, there is a need for a vertebral body spacer that is capable of obtaining a locking effect without the need for additional components such as locking screws.
In certain preferred embodiments of the present invention, a vertebral body spacer includes a main body having an upper end including a first concave socket and a lower end including a second concave socket. A first endplate is secured to the upper end of the main body and includes an underside having a convex projection adapted to form a ball and socket arrangement with the first concave socket. A second endplate is secured to the lower end of the main body and includes an underside having a convex projection adapted to form a ball and socket arrangement with the second concave socket.
In certain preferred embodiments, the upper end of the main body may include an upper edge defining first and second planes that are angled relative to one, and the lower end of the main body may include a lower edge defining first and second planes angled relative to one another. The first and second planes of the upper edge preferably intersect one another at an upper end apex and the first and second planes of the lower edge preferably intersect one another at a lower end apex. The upper apex desirably includes at least one retaining clip projecting therefrom for securing the first endplate to the upper end of the main body and the lower apex includes at least one retaining clip projecting therefrom for securing the second endplate to the lower end of the main body. In highly preferred embodiments, the upper apex includes a pair of retaining clips spaced from one another for pivotally securing the first endplate and the lower apex includes a pair of retaining clips spaced from one another for pivotally securing the second endplate. The first and second angled planes of the upper edge preferably limit pivotal movement of the first endplate and the first and second angled planes of the lower edge limit pivotal movement of the second endplate.
In certain preferred embodiments, the first endplate includes an upper side having teeth for engaging bone, such as the face of a vertebral body, and the second endplate includes an upper side having teeth for engaging bone. The first endplate also preferably has a central opening and a peripheral flange surrounding the central opening, the peripheral flange having at least one opening adapted to facilitate bone fusion. The second endplate, which may be substantially similar in size and shape as the first endplate, also preferably has a central opening and a peripheral flange surrounding the central opening, the peripheral flange having at least one opening adapted to facilitate bone fusion.
Each endplate preferably includes at least one retaining clip aperture adapted for receiving one of the retaining clips for securing the endplate with the main body.
In certain preferred embodiments, the main body is elongated and has an outer surface that is curved. In other preferred embodiments, the main body is substantially cylindrical in shape. The main body may also be elliptical, or have any other geometric shape. In one particular preferred embodiment, the main body has a longitudinal axis and the first and second concave sockets are coaxial about the longitudinal axis. The first and second angled planes at the upper end of the main body form an angle of approximately 5-25 degrees, and more preferably an angle of approximately 10-20 degrees. The main body desirably has a cross-sectional diameter of approximately 10-30 mm, and the endplates have a diameter of approximately 30-50 mm. In other preferred embodiments, the endplates have a diameter of approximately 35-40 mm.
The main body and the first and second endplates are desirably made of biocompatible materials, such as titanium, stainless steel, alloys and combinations thereof. The biocompatible material may also comprise polymeric materials.
The central opening of the first endplate desirably provides communication between the first socket and an exterior of the spacer. The central opening of the second endplate desirably provides communication between the second socket and an exterior of the spacer.
In operation, the spacer is positioned between the opposing faces of vertebrae. The endplates are pivotable when the spacer is in a first no-load state and are locked from pivotal movement when the spacer is in a second load state. Once pressure is applied to the endplates, the ball-and-socket joints are locked due to the blockage of the convex projections of the endplates in the concave sockets. After being positioned between two vertebrae, the endplates are desirably oriented for pivoting in a sagittal plane of a spine.
In other preferred embodiments of the present invention, a vertebral body spacer includes a main body having an upper end and a lower end, the upper end having a first concave socket and an upper edge surrounding the first concave socket defining first and second planes angled relative to one another, the lower end having a second concave socket and a lower edge surrounding the second concave socket defining first and second planes angled relative to one another. The spacer also preferably includes a first endplate pivotally secured to the upper end of the main body for pivoting between the first and second planes of the upper edge, the first endplate including an underside having a convex projection adapted to engage the first concave socket. The spacer also preferably includes a second endplate pivotally secured to the lower end of the main body for pivoting between the first and second planes of the lower edge, the second endplate including an underside having a convex projection adapted to engage the second concave socket. The convex projections preferably form ball and socket joints with the respective first and second concave sockets.
The upper edge desirably includes at least one retainer clip projecting therefrom for pivotally securing the first endplate to the main body, and the first endplate desirably includes at least one retainer clip aperture extending therethrough, the at least one retainer clip being passable therethrough for pivotally securing the first endplate to the main body. The first endplate preferably includes a series of apertures extending therethrough for receiving bone growth material and facilitating spinal fusion.
The lower edge desirably includes at least one retainer clip projecting therefrom for pivotally securing the second endplate to the main body, and the second endplate desirably includes at least one retainer clip aperture extending therethrough, the at least one retainer clip being passable therethrough for pivotally securing the second endplate to the main body. The second endplate preferably includes a series of apertures extending therethrough for receiving bone growth material and facilitating spinal fusion.
These and other preferred embodiments of the present invention will be described in more detail below.